Method of enhancing adhesion strength of BSG film to silicon nitride film

ABSTRACT

A method of enhancing adhesion strength of a boro-silicate glass (BSG) film to a silicon nitride film is provided. A semiconductor substrate with a silicon nitride film formed thereon is provided. The silicon nitride film is then exposed to oxygen-containing plasma such as ozone plasma. A thick BSG film is then deposited onto the treated surface of the silicon nitride film. By pre-treating the silicon nitride film with ozone plasma for about 60 seconds, an increase of near 50% of Kapp of the BSG film is obtained.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor manufacturingtechnique. More particularly, the present invention relates to a methodof enhancing adhesion strength of a boro-silicate glass (BSG) film to asilicon nitride film. The method according to the present invention caneffectively prevent peeling of the BSG film from the silicon nitridefilm during or after a dry etching process, and is capable ofintegrating with standard semiconductor manufacturing processes.

[0003] 2.Description of the Prior Art

[0004] During the manufacturing of semiconductor devices, a number offilm deposition and etching processes are involved. As known by thoseskilled in the art, adhesion property between films in a semiconductorwafer is one of the most important factors that affects yield of thesedevices. Please refer to FIG. 1 to FIG. 5. FIG. 1 to FIG. 5 areschematic diagrams depicting a prior art method of forming a deep trenchon a semiconductor substrate 10. As shown in FIG. 1, a pad oxide layer12 and a silicon nitride film 14 are provided on the semiconductorsubstrate 10. Typically, the silicon nitride film 14 is formed by usinglow-pressure chemical vapor deposition (LPCVD). The silicon nitride film14 has a thickness of about 1 000 to 2000 angstroms.

[0005] As shown in FIG. 2, a thick boro-silicate glass (BSG) film 16 isthen deposited onto the silicon nitride film 14. The BSG film 16 is usedas a hard mask film in the succeeding dry etching processes. Typically,the BSG film 16 has a thickness of about 7,500 angstroms to 15,000angstroms and a boron concentration of about 5.5% in weight.

[0006] As shown in FIG. 3, a patterned photoresist layer 18 is coated onthe BSG film 16. The photoresist layer 18 has openings 19 that definethe location and pattern of deep trenches to be formed in thesemiconductor substrate 10. As shown in FIG. 4, a first dry etchingprocess is carried out to etch the BSG film 16 and the silicon nitridefilm 14 through the openings 19, thereby forming openings 21 in thefilms 16 and 14. Subsequently, as shown in FIG. 5, a second dry etchingprocess is performed to etch the pad oxide layer 12 and thesemiconductor substrate 10 by using the BSG film 16 as a hard mask film,thereby forming deep trenches 23.

[0007] However, as indicated by numeral 25 in FIG. 5, edge peeling isfrequently observed in the interface between the BSG film 16 and thesilicon nitride film 14 around the deep trenches 23. The peelingproblems, which might lead to costly failure of deep trench patterntransfer, usually occur during the dry etching processes. One approachto solving the problem of peeling between the BSG film 16 and theunderlying silicon nitride film 14 is to reduce the boron concentrationof the BSG film 16 down to a value of below 5% in weight. Unfortunately,such a reduced boron concentration in the BSG film 16 will causedifficulty in removing the BSG film 16 in the follow-up cleaningprocedures. As known by those skilled in the art, the higher the boronconcentration in the BSG film 16 is, the easier the BSG film 16 can beremoved in a wet cleaning procedure that employs a typical etchingsolution such as H₂SO₄/HNO₃ mixture.

[0008] Consequently, there is a strong need to provide a method that iscapable of maintaining the boron concentration in the BSG film 16 at anacceptable level, while enhancing the adhesion strength of the BSG film16 to the silicon nitride film 14. Further, according to the prior artdeep trench process, no surface treatment is performed on the siliconnitride film 14 before the deposition of the BSG film 16.

SUMMARY OF INVENTION

[0009] It is therefore a primary objective of the claimed invention toprovide a semiconductor manufacturing method that is able to enhance theadhesion strength of BSG film to silicon nitride film.

[0010] Another objective of the claimed invention is to provide areliable deep trench process.

[0011] According to the claimed invention, a method is provided forenhancing adhesion strength of BSG film to silicon nitride film. Asemiconductor substrate with a silicon nitride film formed thereon isprovided. The silicon nitride film is then exposed to oxygen-containingplasma. A thick BSG film is then deposited onto the treated surface ofthe silicon nitride film. By pre-treating the silicon nitride film withthe oxygen-containing plasma, the BSG film may have a boronconcentration of between 5% and 8% in weight.

[0012] Further, the silicon nitride film may be formed by using LPCVD,plasma-enhanced CVD (PECVD), or high-density plasma CVD (HDPCVD). Theoxygen-containing plasma comprises mixed gas plasma of ozone and oxygen,oxygen plasma, NO plasma, N₂O plasma, or mixed gas plasma of ozone andinert gases.

[0013] These and other objectives of the claimed invention will no doubtbecome obvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment, which isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0014]FIG. 1 to FIG. 5 are schematic diagrams depicting a prior artmethod of forming a deep trench on a semiconductor substrate.

[0015]FIG. 6 and FIG. 7 are schematic diagrams showing a method offorming a deep trench on a semiconductor substrate according to thepresent invention.

[0016] Table 1 illustrates the Kapp values of BSG films obtained by amodified edge lift-off test.

DETAILED DESCRIPTION

[0017] Please refer to FIG. 6 and FIG. 7. FIG. 6 and FIG. 7 areschematic diagrams showing a method of forming a deep trench on asemiconductor substrate according to the present invention. First, asshown in FIG. 6, a semiconductor substrate 30 having a pad oxide layer32 and a silicon nitride film 34 formed thereon is provided. The siliconnitride film 34 may be formed by using low-pressure chemical vapordeposition (LPCVD), plasma-enhanced CVD (PECVD), or high-density plasmaCVD (HDPCVD). Typically, the silicon nitride film 34 has a thickness ofbetween 1000 angstroms and 2000 angstroms. In the preferred embodimentof this invention, the silicon nitride film 34 is formed by using LPCVD.

[0018] Still referring to FIG. 6, after depositing the silicon nitridefilm 34, a surface treatment step for the silicon nitride film 34 iscarried out. The surface treatment step comprises usingoxygen-containing plasma 50 to bombard the exposed surface of thesilicon nitride film 34. The oxygen-containing plasma 50 comprises mixedgas plasma of ozone and oxygen, oxygen plasma, NO plasma, N₂O plasma, ormixed gas plasma of ozone and inert gases. According to the preferredembodiment of this invention, O₃/O₂ plasma that is created under a highfrequency radio frequency (HFRF) of between 1 and 9 W/cm² is used totreat the surface of the silicon nitride film 34 for 5 seconds to 20minutes. Preferably, the O₃/O₂ plasma has an ozone/oxygen concentrationof about 2% to 50% in weight. As shown in FIG. 7, a thick BSG film 36 isdeposited onto the pre-treated silicon nitride film 34. The BSG film 36has a thickness of about 7,500 angstroms to 15,000 angstroms and a boronconcentration of about 5.53% in weight. The remaining steps of forming adeep trench in the semiconductor substrate 30 are similar to the priorart processes and are therefore omitted hereinafter. It is advantageousthat by pre-treating the silicon nitride film 34 with theoxygen-containing plasma 50, the BSG film 36 may have a boronconcentration of up to 7% to 8% in weight without affecting the adhesionstrength of the BSG film to silicon nitride film. TABLE 1 FILMCONDITIONS Kapp (Mpa-m^(1/2)) 13k BSG film (B% = 5.53% in weight) 0.3101SiN film without surface treatment 13k BSG film (B% = 5.53% in weight)0.4688 SiN film pre-treatedwith O₃ plasma (60 sec)

[0019] Please refer to table 1. Table 1 shows comparison of the Kappvalues of BSG films obtained by a modified edge lift-off test. As shownin table 1, the Kapp values are obtained by testing the BSG films havinga thickness of about 1 3,000 angstroms and a boron concentration ofabout 5.53% in weight. It is clear that by pre-treating the siliconnitride film with ozone plasma for about 60 seconds, an increase of near50% of Kapp of the BSG film is obtained.

[0020] Those skilled in the art will readily observe that numerousmodifications and alterations of the device may be made while retainingthe teachings of the invention. Accordingly, the above disclosure shouldbe construed as limited only by the metes and bounds of the appendedclaims.

What Is Claimed Is:
 1. A method of enhancing adhesion strength of a BSGfilm to a silicon nitride film, comprising: providing a semiconductorsubstrate having a silicon nitride film formed thereon; exposing thesilicon nitride film to an oxygen-containing plasma; and depositing aBSG film on the silicon nitride film.
 2. The method of claim 1 whereinthe silicon nitride film is formed by using low-pressure chemical vapordeposition (LPCVD), plasma-enhanced CVD (PECVD), or high-density plasmaCVD (HDPCVD).
 3. The method of claim 1 wherein the silicon nitride filmhas a thickness of about 1 000 to 2000 angstroms.
 4. The method of claim1 wherein the BSG film has a boron concentration of between 5% and 8% inweight.
 5. The method of claim 4 wherein the BSG film has a boronconcentration of about 5.53% in weight.
 6. The method of claim 1 whereinthe thickness of the BSG film is between 7,500 to 1 5,000 angstroms. 7.The method of claim 1 wherein the oxygen-containing plasma comprisesmixed gas plasma of ozone and oxygen, oxygen plasma, NO plasma, N₂Oplasma, or mixed gas plasma of ozone and inert gases.
 8. The method ofclaim 1 wherein the oxygen-containing plasma consists of ozone andoxygen having an ozone/oxygen concentration of about 2% to 50% inweight, and wherein the oxygen-containing plasma is created under a highfrequency radio frequency (HFRF) of about 1 to 9 W/cm².
 9. The method ofclaim 1 wherein the silicon nitride film is exposed to theoxygen-containing plasma for about 5 seconds to 20 minutes.
 10. A methodof manufacturing a deep trench, comprising: providing a substrate;forming an oxide layer on the substrate; depositing a silicon nitridefilm over the oxide layer; exposing the silicon nitride film to anoxygen-containing plasma for a predetermined time period; depositing aBSG film over the silicon nitride film; and dry-etching the substrate toform a deep trench by using the BSG film as a hard mask.
 11. The methodof claim 10 wherein the silicon nitride film is formed by usinglow-pressure chemical vapor deposition (LPCVD), plasma-enhanced CVD(PECVD), or high-density plasma CVD (HDPCVD).
 12. The method of claim 10wherein the silicon nitride film has a thickness of about 1 000 to 2000angstroms.
 13. The method of claim 10 wherein the BSG film has a boronconcentration of between 5% and 8% in weight.
 14. The method of claim 10wherein the BSG film has a boron concentration of about 5.53% in weight.15. The method of claim 10 wherein the thickness of the BSG film isbetween 7,500 to 15,000 angstroms.
 16. The method of claim 10 whereinthe oxygen-containing plasma consists of ozone and oxygen having anozone/oxygen concentration of about 2% to 50% in weight, and wherein theoxygen-containing plasma is created under a high frequency radiofrequency (HFRF) of about 1 to 9 W/cm².
 17. The method of claim 10wherein the oxygen-containing plasma comprises mixed gas plasma of ozoneand oxygen, oxygen plasma, NO plasma, N₂O plasma, or mixed gas plasma ofozone and inert gases.
 18. The method of claim 10 wherein thepredetermined time period is between 5 seconds and 20 minutes.